What causes the error when it says the widget does not exist when I can clearly see it with webdav?
Customer Portal (CP)
1) You are getting that error message because that widget is not activated yet.
You need to go into your Administrator Dashboard, Choose Widgets->Widgets Versions. Then under the Widgets tab scroll down to the output/ProdcutCatalogDisplay widget and click on it. You should see an Activate this version button in the right side of the window. Click on this button.
Next, when you are ready to stage, after you Select your files, under Version Changes, there is an option down at the bottom that says...Push all framework and widget version changes? You need to select YES then continue with the rest of staging and promoting.
This should solve the error of staging failing and allow you to successfully promote everything to production.
2) You are getting that error message because that widget is no longer available to the version of CP you are using.